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M4 Stainless Steel 316 Sunk Screw
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Name: M4 Stainless Steel 316 Sunk Screw
Standard: DIN7991
Material: SS316
Size: M4
Lenght: 6 mm
Surface: Natural color
Standard: DIN7991
Material: SS316
Size: M4
Lenght: 6 mm
Surface: Natural color
Quantity
M4 Stainless Steel 316 Sunk Screw, manufactured to DIN 7991, in SS316 grade, 6 mm long, resistant to chloride-ion corrosion, deep-recessed slot for anti-loosening, purpose-built for yachts, coastal PV and food equipment—install once, zero maintenance, field-proven by million-piece exports to Europe and the US.
The cost gap between 316 and 304 countersunk bolts is rooted in three links: alloying elements, melting practice and downstream fabrication. Taking September 2025 domestic mill list prices as reference, 304 cold-heading wire (φ6.5 mm) is quoted at RMB 15.2/kg tax-incl., whereas 316 (2 % Mo) wire is RMB 21.8/kg, driven by the USD 45 000/t molybdenum price—a 43 % raw-material gap alone. Moly accounts for 18 % of 316’s material cost and is highly volatile: the 2023 Mo rally of 50 % y/y lifted the ex-works price of 316 bolts such as M4 Stainless Steel 316 Sunk Screw by more than 30 %.
In machining, 316 is 15 HV harder than 304: cold-heading dies wear 15 % faster, tapping speed drops 12 %, and press output falls from 180 to 155 pcs/shift; labour and electricity add about RMB 0.08 per piece. External cold-heading + thread-rolling for 304 countersunk M6×20 is RMB 0.35/pc; the same spec in 316 is RMB 0.46/pc, a 31 % processing premium. Scaled to M4 Stainless Steel 316 Sunk Screw, the uplift is proportionally identical.
Surface treatment: 304 usually receives soap or passivation only (RMB 0.02/pc); 316, required to survive 1 000 h salt-spray, needs extra electropolishing to remove free iron, lifting cost to RMB 0.07/pc. This step is non-negotiable for M4 Stainless Steel 316 Sunk Screw.
Roll-up: M6×20 countersunk bolt ex-works—304: RMB 0.85/pc (mat. 0.48 + proc. 0.35 + finish 0.02); 316: RMB 1.31/pc (0.69 + 0.46 + 0.07), a RMB 0.46/pc or 54 % gap. The same raw-material, processing and finishing premiums apply proportionally to M4 Stainless Steel 316 Sunk Screw.
Logistics & inventory, often ignored: the higher unit price of 316 increases capital tied up per turnover. At six stock-turns p.a. and 5 % cost of capital, 316 carries a hidden finance charge of RMB 0.011/pc, 2.2× that of 304; for the still higher-priced M4 Stainless Steel 316 Sunk Screw the difference is even starker.
Bring service life into total cost of ownership: in C5 high-salinity atmosphere 304 countersunk bolts show pitting within three years and must be replaced, whereas M4 Stainless Steel 316 Sunk Screw and other 316-grade fasteners deliver 25 years maintenance-free. Valuing one offshore replacement at RMB 200 labour plus RMB 1 000 downtime, the 304 life-cycle cost is RMB 1 200.85 against RMB 1.31 for 316—making 316 two orders of magnitude cheaper.
Therefore, although 316 costs ~50 % more upfront, in coastal, chemical or food applications where chloride ion >5 000 ppm the “material premium” of M4 Stainless Steel 316 Sunk Screw is far lower than the “failure penalty”, and the all-in cost is decisively superior.
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